Many types of tobacco smoke modifying agents are known in the art to be added to smoking products to modify the tobacco smoke. For example, flavorants are added to smoking products to enhance their taste and to compensate for variations in tobacco quality and blend. Although flavorants are traditionally applied to the tobacco portion of the smoking product, this practice results in only a small fraction of the flavorant ever reaching the smoker. Most of a flavorant added to the tobacco is lost in the sidestream smoke produced during the static burn period of the smoking article or is removed by the smoke filter. The low flavorant delivery efficiencies associated with application on tobacco necessitates the use of relatively large quantities of flavorant to achieve the desired effect. Because many of these flavorants, such as menthol, for example, are expensive, inefficient utilization can add significantly to the cost of the smoking product. In addition, flavorants applied to the tobacco are subjected to the high heat of combustion which can undesirably alter their organoleptic characteristics.
In response to these problems, there has been substantial effort to apply flavorants to the filter. It was shown many years ago that smoke aerosols could transport significant quantities of relatively non-volatile materials from a structure of moderate surface area, even though a gas at a comparable temperature is ineffective in this regard. Attempts at the practical implementation of this phenomenon using cellulose acetate filters revealed, however, that although aerosols transported flavorant very efficiently from freshly made filters, this advantage was lost as the flavorant diffused away from the surface and into the bulk of the filter fibers.
Efforts to solve this problem by using polymers impermeable to the flavorants, such as polypropylene, eliminated the time dependence of flavorant delivery observed with cellulose acetate filters, but did not permit the development of a functional flavorant delivery system. The causes of this failure were, first, the flavorant delivery efficiencies for these nonpermeable polymer systems were too low to be useful, and second, impermeable filter media had no affinity for the flavorant which consequently diffused to the tobacco where it endured the same fate as flavorants applied directly to the tobacco.
In spite of years of concerted effort, neither the cigarette nor the filter material industry has developed an efficient general flavorant delivery system that does not absorb or lose the flavorant over time.
Prior art of this area reflects a strong interest in technology for the efficient and consistent delivery of tobacco smoke modifying agents, especially flavorants. However, the abundant patented technologies for flavorant delivery almost invariably employ one of the following four strategies:
1. A flavorant is contained by some physical means and is released either by mechanical destruction of the containment apparatus or by controlled leakage (see, for example, U.S. Pat. Nos. 3,219,041; 3,297,038; 3,339,557; and 4,720,423).
2. A flavorant is adsorbed on a material whose surface has been customized so that the flavorant will be displaced by the moisture or heat in the smoke (see, for example, U.S. Pat. Nos. 3,236,244; 3,280,823; and 4,662,384).
3. A flavorant is absorbed in a polymeric matrix and is then released by the plasticizing action of moisture or heat in the smoke (see, for example, U.S. Pat. Nos. 4,662,384; 3,144,024; and 4,729,391). A portion of the prior art in this area addresses the concept of modifying the fiber shape or filter geometry of current cellulose acetate filters to achieve improved flavorant containment or delivery (see, for example, U.S. Pat. Nos. 4,180,536, 4,619,279; and 4,821,750).
4. A flavorant undergoes a chemical reaction with another compound to form a new compound that will regenerate the original flavorant upon thermal decomposition (see U.S. Pat. No. 3,288,146).
Although there is substantial prior art, virtually every implementation of this art possesses limitations which render its commercial application impractical. These limitations are largely defined by the flavorant delivery strategy employed and will, therefore, be so organized here.
Mechanical or physical flavorant containment devices which are incorporated into the filter and ruptured prior to smoking are very complex and expensive to produce. They introduce significant variation into the performance of the smoking article because of inconsistencies in the pattern of their breakage, and they interfere with the normal function of the filter by altering smoke flow through the filter. They also increase the effort and complexity to the consumer who uses the product.
Adsorbed flavorants which are incorporated into the filter and released by the heat or moisture content of the smoke are not efficiently delivered until enough of the smoking article has been consumed to allow adequate moisture and heat to reach the filter. As a consequence, the flavorant is not available to augment smoke taste during the first few puffs, when it is generally acknowledged as being most needed. In addition, absorbants must be customized to achieve the desired release characteristics for each flavorant and, therefore, are not useful for delivering naturally occurring flavoring materials which consist of large numbers of independent chemical entities.
Absorbed flavorants which are dissolved in polymer matrices and released by the plasticizing action of moisture or heat in the smoke are subject to the same limitations as adsorbed flavorants. In addition, absorbed flavorants are subject to time dependent losses in delivery efficiency because of diffusion of the flavorant into the bulk of the fiber polymer. This limitation is especially evident when a conventional cellulose acetate filter is used as the flavorant absorber.
Derivatized flavorants are almost always inappropriate for use in filter flavorant delivery systems because relatively high temperatures are required for their release. Derivatized flavorants are, therefore, typically applied to the tobacco portion of the smoking product, where the liberated flavorant produced during combustion is subject to chemical alteration and loss during the static burn period of the smoking article. The development of derivatized flavorants is highly specific for each flavorant and, therefore, excludes naturally occurring flavoring materials which are composed of a large number of independent chemical entities.
Although flavorants are the most commonly used tobacco smoke modifying agents, selective removal additives can also serve as tobacco smoke modifying agents. In contrast to flavorants, selective removal additives modify tobacco smoke by removing, rather than adding, certain compounds or classes of compounds. Selective removal additives are applied to the filter and, therefore, like flavorants, can be absorbed by the filter fibers and lose their effectiveness. Here, too, significant improvements in the performance of selective removal additives could be achieved by overcoming the limitations imposed by the substrate to which the additives are applied.
We have unexpectedly discovered that if spontaneously wettable fibers described below are combined with a conventional additive, and used in a tobacco smoke filter in accordance with this invention, enhanced flavor and filtering are realized. Preferably, the spontaneously wettable fibers are formed into a nonwoven web and used as a wrap around a conventional tobacco smoke filter, i.e., as a circular layer between the conventional fibrous filter and the conventional filter wrap.
Patents of interest further include U.S. Pat. No. 4,807,809 which relates a filter rod making apparatus, and U.S. Pat. No. 5,105,834 which relates to cigarette filter containing a spray extract.